Halve and seed the chilies. Peel the garlic. Peel and shred the ginger. Finely slice the tender, innermost leaves of the lemon grass. Grind the coriander seeds or crush them in a mortar. Blitz it all to a thick paste in a food processor with the coriander leaves and any well scrubbed roots, plus the tumeric. You may need a few tablespoons of vegetable oil to help it go round but add as little as you can.

Place a fairly deep pan over moderate heat, add half the spice paste (keep the other half in the fridge for tomorrow) and fry it, movingit round the pan, for a minute or so, then pour in the stock, coconut milk, and a splash of soy sauce -- let it come to the boil. Turn the heat down and let the soup simer for ten minutes. Meanwhile cook the noodles briefly in boiling water and drain them.

Divide the noodles between four large, deep bowls and ladle over hot soup. Sprinkle with mint leaves.